This invention relates in general to vehicle drum brake assemblies and in particular to an improved structure for a parking and emergency brake actuating lever adapted for use in such a vehicle drum brake assembly.
Most vehicles are equipped with a brake system for retarding or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. The brake assemblies can be actuated by hydraulic, pneumatic, or mechanical pressure generated by an operator of the vehicle depressing a foot pedal, pulling a hand lever, and the like. The structure and operation of both drum brake assemblies and disc brake assemblies, as well as the actuators therefor, are well known in the art.
A typical drum brake assembly includes a backing plate which is secured to a fixed, non-rotatable component of the vehicle, such as the vehicle axle housing. A pair of opposed arcuate brake shoes are supported on the backing plate for selective movement relative thereto. The brake drum assembly further includes a cylindrical brake drum which is secured to the vehicle wheel for rotation therewith. The interior of the brake drum is hollow, defining an inner cylindrical braking surface. The brake drum is disposed adjacent to the backing plate such that the brake shoes extend within the hollow cylindrical interior thereof. To effect braking action, the brake shoes are moved outwardly apart from one another so as to frictionally engage the inner cylindrical braking surface of the brake drum. Such frictional engagement causes retarding or stopping of the rotational movement of the brake drum and, therefore, the wheel of the vehicle in a controlled manner.
One or more actuating mechanisms are provided in the brake drum assembly for selectively moving the brake shoes outwardly apart from one another into frictional engagement with the inner braking surface of the brake drum. Usually, a hydraulic or pneumatic service brake mechanism is provided for selectively actuating the drum brake assembly under normal operating conditions. Such a service brake mechanism can include a hydraulic cylinder having a pair of opposed pistons which abut and move the brake shoes apart from one another into frictional engagement with the inner braking surface of the brake drum. A mechanically actuated parking and emergency brake mechanism is also usually provided for selectively actuating the drum brake assembly. The parking and service brake mechanism can include an actuating lever pivotally supported on one of the brake shoes. The actuating lever is connected to a cable which, when pulled, moves the brake shoes apart from one another into frictional engagement with the inner braking surface of the brake drum.
As mentioned above, the actuating lever of the parking and emergency brake mechanism is pivotably supported on one of the brake shoes. Two well known structures have been used in prior art brake assemblies to accomplish this. In the first prior art structure, a pivot pin assembly is provided which includes a pivot pin having an enlarged head and a reduced diameter body. The body of the pivot pin is inserted through respective aligned apertures formed through the actuating lever and a web portion of the brake shoe. An E-clip or similar fastener is then installed in a groove formed about the end of the body of the pivot pin to retain it in the apertures such that the actuating lever is pivotably supported on the brake shoe. In the second prior art structure, the actuating lever is formed having an bent tang at one end which is loosely received within an enlarged opening formed through a web portion of the brake shoe. As a result, the actuating lever is pivotably supported on the brake shoe. Although both of these prior art structures have functioned satisfactorily, they have been found to have certain drawbacks. The first prior art structure provides a secure support for the actuating lever on the brake shoe without any undesirable looseness or play therebetween, but requires the use and installation of several small and separate parts. This extra structure and installation time adds cost and complexity to the brake assembly. The second prior art structure requires no additional parts or significant installation time, but does result in a significant amount of undesirable looseness or play between the actuating lever and the brake shoe. Thus, it would be desirable to provide an improved structure for a parking and emergency brake actuating lever which provides a secure support for the actuating lever on the brake shoe without any undesirable looseness or play therebetween, and which requires no additional parts or significant installation time.